In response to "The Myth of RAM" https://news.ycombinator.com/item?id=12383012
It so happens that a large part of my PhD was on this very subject. The result I've got N log(N), this is more visible when you get to larger RAM (I had 0,5 TB RAM at the time). We have an empirical result, a justification and a rigorous predictive model.
The reason has to do with hashing, but a different type: TLB.
Feel free to take a look at a free copy at http://arxiv.org/abs/1212.0703 where we establish the VAT cost model.